Modern motor vehicles employ a plurality of feedback control and control systems to control wheel performance. An anti-lock control system, a traction control system having brake intervention and/or engine intervention, an operating dynamics controller having brake intervention and/or engine intervention, and an electrically controlled braking system (brake-by-wire) are some examples.
German Patent Application No. 196 51 154 describes a system in which the temperature of the hydraulic fluid and, thus, the temperature of the hydraulic unit of the braking system are estimated based on the after-run behavior of a pump supplying the hydraulic fluid. The valve opening times, especially in reference to the pressure build-up, are then changed as a function of the estimated temperature, so that the pressure change dynamics in the wheel brakes do not deteriorate considerably at low temperatures. However, determining the temperature of the hydraulic fluid or the hydraulic unit on the basis of the pump's after-run behavior is a relatively inaccurate method, so that this information cannot be used satisfactorily for exact control of a braking system.
European Patent No. 166 178 describes a traction control system which actuates the brakes and/or influences the engine torque when a slip threshold is exceeded due to the slip of at least one drive wheel. The manner in which the threshold values and/or the extent of the torque intervention are established results from a compromise between traction and stability, which is maintained over the entire temperature range.